The present invention relates generally to signal burst acquisition and more particularly to a method and system for acquisition of a time stamped signal.
Emergency 911 service is rapidly becoming essential in today""s society. One of the compelling reasons for using the existing landline emergency 911 system is the ability to trace the caller""s location. Using databases in the telephone network switches, the caller""s location is determined and made available to the emergency services. In the event the caller is unable to inform the operator of their location, the ability to trace the call is invaluable.
The explosive growth of mobile phones, however, causes complications for emergency 911 services. While mobile users may call the 911 operator just as they would using a landline phone, there is no ability to trace the exact location of the mobile caller. The emergency 911 operator currently can only trace the mobile call to the base station closest to the mobile caller is using.
Mobile systems with the ability to locate mobile callers are known as enhanced 911 wireless or E911 systems. One known approach to determine a mobile caller""s location involves using an improved handset. These handset improvements, however, involve improved handset circuitry that increases the cost of the handsets. Further, the extra circuitry requires extra battery power. Moreover, deployment of the improvement takes time since it depends on the users upgrading their handsets.
Another approach would not modify the handsets, thereby avoiding the problems stated above. The so-called network approach involves modifying the base stations. One such approach is known as Time Difference Of Arrival or TDOA. One method of TDOA involves measuring the Time Of Arrive (TOA) of the mobile""s signals at multiple base stations. The TOAs are then sent to the Central Office and subtracted to get a measurements of TDOA between base stations. These TDOA parameters are then used to locate the mobile""s position using standard hyperbolic locating techniques.
Measuring the TOAs involves detecting the starting position of the received signal and also providing a time stamp. Conventionally, this is known as burst acquisition and clock recovery. Conventional burst acquisition and clock recovery algorithms, however, do not capture time delay information. Once the open-eye samples are obtained, the original raw data is discarded. There is a timing ambiguity the open eye samples are mapped to the original raw data. Thus, the conventional burst acquisition and clock recovery algorithms cannot be used for mobile locating.
Therefore, clearly there is a need to acquire a time stamped signal burst while preserving timing information.
The invention is directed to a method and system for acquisition of a time stamped signal burst while preserving timing information.
According to one aspect of the present invention, there is provided a system for acquisition of a time stamped signal burst while preserving timing information. The system includes a first framer, an offset frequency compensator and a second framer. The first framer is for framing a buffered signal burst using least mean squares tuning to produce a first time stamp. The offset frequency compensator is for substantially removing a frequency offset from the first time stamp to produce a rough signal burst. The second framer is for framing the rough signal burst using least mean squares tuning to produce a fine signal burst and a second time stamp, the second time stamp being more reliable than the first time stamp.
According to a further aspect of the present invention, there is provided a method for acquisition of a time stamped signal burst while preserving timing information including the steps of framing using LMS and compensating for frequency offset An advantage of the invention is increased reliability of the time stamp of the acquired signal burst.